1. Field of the Invention
The present invention relates, in general, to a decontamination process and, in particular, to a process of decontaminating zirconium-based alloy claddings tubes of nuclear reactor fuel rods.
2. Background Information
Fuel rods of nuclear reactor assemblies consist of UO.sub.2 pellets and a zirconium-based alloy (e.g. Zircaloy) cladding tube. The rods are made by stacking the UO.sub.2 pellets into cladding tubes approximately 13 feet in length. During the process of loading the pellets into the tube, UO.sub.2 can become embedded into the Zircaloy or zirconium surface. Deposition of UO.sub.2 can also occur as the rods are transported through the factory or as UO.sub.2 pellets are removed from defective rods. The cladding material must then be decontaminated before it can be recycled for future use in the production of reactor fuel bundles.
Typically, decontamination of Zircaloy begins with the high temperature oxidation of UO.sub.2 to form U.sub.3 O.sub.8. In a subsequent step, the particulate U.sub.3 O.sub.8 is reacted with concentrated nitric acid (about 3 molar). This step dissolves the uranium contaminant as well as the zirconium base metal and results in the formation of uranyl nitrate and zirconium nitrate. This method presents significant handling problems since the resulting waste solutions are highly corrosive. In addition, the zirconium nitrate formed during the process poses a significant fire and explosion hazard.